The invention is directed to a continuously operating gas analyzer with a detector which is connected to a measurement amplifier and with regulated measurement gas feed. The measurement gas feed includes a measurement gas pump at the detector input or detector output, a first choke which is connected in the measurement gas line upstream of the detector, a second choke which is connected in parallel with the series connection of the first choke and detector as a bypass, a third choke which is arranged in the measurement gas line and connected in series upstream of the branch point of the lines leading to the first and second chokes, and a pressure regulator which maintains constant pressure at the common connection point of the three chokes. A measurement gas regulating arrangement of this type is described in DE 2 932 436.
Gas analyzers for measuring the concentration of a gas component are generally limited to a determined range of concentration, since the response curve outside this concentration range is not linear or, e.g., passes into saturation. This concentration range determines a so-called standard measurement range within which operation is normally effected. Many steps are known for expanding this measurement range or for detecting gas concentrations lying outside the standard measurement range with sufficient accuracy. In UV/VIS or IR spectroscopy, for example, the length of the cell can be decreased to reduce the optical path length. Further, it is known to dilute a very highly concentrated measurement gas flow in a defined manner.
U.S. PAT. NO. 3,975,947 describes a control loop by which concentrations of a substance in a sample flow can be determined in a continuous manner. The detector signal regulates a dilution flow in such a way that the signal assumes a constant value which corresponds in turn to a predetermined reference value. In order to maintain this reference value, the substance to be measured must be fed into the measurement gas flow upstream of the detector in the event that the sample flow does not contain this substance. The concentration to be determined can then be derived directly from the control variable of the regulator. The aim of the process is a constant calibration of the detector during measurement.
EP 71 132 describes a gas analyzer in which a flushing or scavenging gas which is free of measurement gas can be delivered to a cavity upstream of the sensor by means of a pump. The sensor is connected with a measurement amplifier arranged downstream together with the pump as a control loop which switches on the pump when the sensor signal reaches a threshold value and increases the output of the pump as the sensor signal increases. An overloading of the electrochemical sensor due to excessively high gas concentrations can be prevented by these steps. In principle, a given standard measurement range can also be expanded in the same manner. The present invention is based on this idea.